1. Field of the Invention
This invention relates, generally, to the art of prosthetics. More particularly, it relates to improvements in prosthetic feet.
2. Description of the Prior Art
During normal ambulation, the first part of a foot to contact the ground is the trailing end of the heel. This initial contact between heel and ground is known as the xe2x80x9cheel strike.xe2x80x9d The trailing end of the heel is soft and thus cushions the heel strike to at least some extent. The hard bottom of the heel is the next part of the foot to strike the ground; its hardness allows it to support the entire weight of the body. The foot continues to rotate in the well-known way until the toes xe2x80x9cpush offxe2x80x9d at the end of a step.
Early prosthetic feet are quite rigid and provide little or no cushion to the impact on the ground at the moment of xe2x80x9cheel strikexe2x80x9d and little or no elastic response at xe2x80x9cpush off.xe2x80x9d The shock of impact is thus transmitted directly to the skeletal structure of the user, and the lack of elastic response forces an unnatural gait.
Perhaps the earliest prosthetic foot that provides an elastic response at heel strike and push off is disclosed in U.S. Pat. No. 4,547,913 to Phillips, assigned to Flex Foot, Inc. Multiple versions of that device have been developed. The original version is formed of a carbon fiber epoxy matrix consisting of a one-piece combination pylon upper and a one-piece sole. Mechanical fasteners interconnect the upper and the sole. In a second embodiment, the pylon is a round hollow tube and is connected by mechanical fasteners to a rectangular-shaped upper. A third version is like the first except that a standard Sach(copyright) foot adapter is employed to connect a standard prosthetic pylon. A fourth version is like the third but has a slightly different geometry. In a fifth version, an elastomeric glue connects the upper and the sole. In additional embodiments, leaf springs or hydraulic cylinders are incorporated into the prosthetic foot.
Although the developments in the art since the mid 1980s have significantly advanced the technology of prosthetic feet, the known prosthetic feet still provide little or no heel elasticity in a direction parallel to the ground. Instead, they provide elastic response in a vertical plane. Thus, although the impact at heel strike is reduced vis a vis the pre-1980""s prosthetic feet, the reduced impact is transmitted vertically to the skeletal structure of the user, and the elastic response in a vertical plane causes a four to six millimeter bounce at heel strike. This vertical response causes an unnatural walk because a healthy human heel is soft at the trailing end where heel strike occurs and is hard on the bottom so that it can support the entire weight of the body. Thus, the normal gait of a human includes a rolling motion as the trailing end of the heel strikes the ground; there is no vertical motion causing the heel to bounce upon ground impact.
Accordingly, there is a need for a prosthetic foot that provides substantial heel elasticity in a direction parallel to the ground.
A healthy human foot rolls on the lateral part of the foot during ambulation. The medial part of the foot provides a cushion and the force required at push off. Thus, there is a smooth transition from heel strike to push off, with no vertical dynamic response of the type that could cause the foot to bounce. Prosthetic feet of the type heretofore known, however, do not provide a smooth transition from heel strike to push off. This lack of a smooth transition produces what is known in the industry as a xe2x80x9cflat spot.xe2x80x9d The presence of a flat spot between heel strike and push off produces an unnatural gait.
More particularly, the dynamic response is primarily vertical at the heel and the toe of a prosthetic foot. There is little or no component of the dynamic response in a horizontal plane as present in a healthy natural foot. The absence of dynamic response in a horizontal plane results in a step like motion going from an elastic vertical motion at heel strike to little or no support at mid-stance (the flat spot), and then again to an elastic vertical motion at push off.
There is a need, therefore, for a prosthetic foot having a dynamic response in a horizontal plane during heel strike, that provides a smooth transition between heel strike and push off to eliminate the flat spot, and that provides a dynamic response in a horizontal plane during push off.
The human foot provides a more rigid support laterally than medially. This design is advantageous because when an instability occurs, the weight of the person shifts from the rigid outer or lateral edge of the foot to the less rigid inner or medial edge. In this way, the prosthetic foot takes advantage of the presence of the natural foot, i.e. , the lateral-to-medial motion experienced at the moment of an instability shifts additional support duties to the natural foot. One major drawback of the heretofore known prosthetic feet is the fact that such feet provide an exactly vertical response during ambulation with no component toward the medial section of the foot. Thus, if an instability in one foot urges the person to fall away from the natural foot, there is no shift of weight toward the medial part of the prosthetic foot as would occur in a natural foot, and the likelihood of a fall is substantially increased.
A prosthetic foot is therefore needed that has differentiated medial and lateral stiffness so that it can respond to instabilities in much the same way as a natural foot.
However, in view of the prior art considered as a whole at the time the present invention was made, it was not obvious to those of ordinary skill in the pertinent art how the identified needs could be fulfilled.
The long-standing but heretofore unfulfilled need for an improved dynamic prosthetic foot is now met by a new, useful, and nonobvious dynamic prosthetic foot having a split upper ankle and a heel with differentiated elasticity. The novel prosthetic foot includes a sole and an ankle part that separates from the sole along a transverse parting line. The transverse parting line is approximately half way between a toe end of the sole and a heel end of the prosthetic foot.
The ankle part includes a gradual upward bend, a horizontal part, and a vertically extending part that provides a pair of transversely spaced apart pylon supports.
The novel prosthetic foot further includes a heel part formed integrally and generally coplanar with the sole.
The heel part includes a central support, a central extension, a lateral heel extension, and a medial heel extension.
The central support has a leading end disposed in underlying, supporting relation to the horizontal part of the ankle part and a downwardly turned return bend formed in a trailing end thereof.
The central extension has a leading end secured to a trailing free end of the central support and a trailing end having a gradual upward bend formed therein.
The lateral heel extension and the medial heel extension are disposed on opposite sides of the central support and the central extension.
Accordingly, the central support, central extension, lateral extension, and medial extension of the heel part provide differentiated responses to impact forces created by ambulation.
A vertically extending slot is formed in the vertically extending part of the ankle part, mid-breadth thereof to divide said vertically extending part into two equal size parts. The two equal size parts form the lateral pylon support and the medial pylon support. The lateral pylon support is adapted for connection to a first prosthetic pylon and the medial pylon support is adapted for connection to a second prosthetic pylon. More particularly, a lateral pylon connector adapted to receive the lateral pylon is secured to the lateral pylon support along a trailing, heel side thereof and a medial pylon connector adapted to receive the medial pylon is secured to the medial pylon support along a trailing, heel side thereof.
The central extension has a trailing end that trails the respective trailing ends of the lateral heel extension and the medial heel extension. The leading end of the central extension is coextensive with the free end of the central support.
In a second embodiment of the invention, elongate lateral and medial pylons supplant the lateral and medial pylon supports and the lateral and medial pylon connectors secured thereto. The lateral and medial pylons are about twenty inches in length and are cut to size as needed by a prosthetist at the time of fitting the novel foot to a patient. The uppermost ends of the lateral and medial pylons are connected to the prosthetic socket that receives the residual limb.
An important object of this invention is to provide a prosthetic foot having heel elasticity in a direction parallel to the ground.
Another important object is to provide a prosthetic foot having a smooth transition from heel strike to push off.
Yet another object is to provide a prosthetic foot having differentiated medial and lateral stiffness so that an instability tends to shift weight from the lateral edge of the prosthetic foot to the medial edge thereof, just as in a natural foot.
These and other important objects, advantages, and features of the invention will become clear as this description proceeds.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts that will be exemplified in the description set forth hereinafter and the scope of the invention will be indicated in the claims.